A 6-pole induction machine is working as an induction generator. If the supply frequency is 60 Hz and the rotor current frequency is 5 Hz, find the speed of the rotor.

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MPPGCL JE Electrical 28 April 2023 Shift 2 Official Paper
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  1. 1400 rpm
  2. 1300 rpm
  3. 1100 rpm
  4. 1200 rpm

Answer (Detailed Solution Below)

Option 2 : 1300 rpm
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Detailed Solution

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Concept

The frequency of EMF induced in an induction motor is given by:

\(f_r=sf_s\)

The speed of an 

where, fr = Rotor induced frequency

fs = Supply frequency

s = Slip

The speed of a 3ϕ induction generator is given by:

\(N_r=N_s(1+s)\)

\(N_r={120f_s\over P}(1+s)\)

Calculation

Given, fr = 5 Hz 

fs = 60 Hz

\(5=s\times 60\)

\(s={1\over 12}\)

 

\(N_r={120\times 60\over 6}(1+{1\over 12})\)

\(N_r=1300 \space rpm\)

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